1. Field of the Invention
The present invention relates to a camera having a circuit carrier on which an objective holder is mounted.
2. Description of the Related Art
As a rule, cameras for vehicles have a circuit carrier on which an objective holder is mounted, which in turn holds an objective. The objective generally includes a lens barrel made of plastic, for instance, and multiple lenses inside the lens barrel, which are set apart by spacers. In addition, an image sensor is indirectly mounted via a sensor support, or also directly on the circuit carrier. The direct mounting of the image sensor is also known as COB (chip on board).
The image sensor has a sensor surface which constitutes the image plane. For proper alignment, an objective axis, i.e., an axis of symmetry of the objective, is to coincide with a surface normal of the sensor surface that sits perpendicularly on the sensor surface, so that the objective axis and the surface normal constitute the optical axis of the camera. Focusing therefore takes place along the optical axis.
Angular tilting between the objective axis and the surface normal leads to a corresponding loss in depth of focus in the particular sectors at the edge of the sensor surface that are shifted out of an ideal focus, and thus at the edge of the image as well. These sectors become myopic or hyperopic. This has a negative effect on the achievable yield in the production since such cameras operate unreliably and may have to be scrapped.
In addition to connection and production tolerances in the production of the camera, the angular tilting of the optical axis with respect to the surface normal also results from a tilting angle of the objective, which, for example, may be caused by tolerance-related shifting or tilting of individual lenses of the objective in relation to each other. This tilting is a variable that characterizes an objective and is also measurable and able to be compensated again by corresponding counter-tilting of the objective. The tilting may be referred to as image shell tilting, since a real object is generally imaged to an image shell (instead of the image plane of the ideal object).
For an adjustment of such counter-tilting it is known to carry out an active alignment during the production process, once the objective holder has been mounted on the circuit carrier; during such an adjustment images of the image sensor of measured objects are read out and their focus is evaluated. The objective is then tilted in its angular position relative to the image sensor until the objective axis essentially lies on the surface normal of the image sensor again and the recorded image is in focus in the edge regions as well, whereupon the configuration is fixated, e.g., by bonding or soldering.
Such a method is performed in multiple steps and requires time and work, since an adjustment and evaluation in all angular and translatory directions (6-axes alignment) takes place.